The invention relates to a circuit to produce a direct current (DC) output from a 3-phase alternating current (AC) source, such as a circuit including a MOSgate driver to drive MOSgated devices in a rectifier circuit.
It is believed that at least some power electronics applications, such as AC motor drive applications, automotive generator applications, and/or switching power supply applications, may include circuits to rectify a sinusoidal voltage source to produce a DC output. The rectifying of the sinusoidal source may be performed, for example, by a diode bridge or by a collection of active switch bridges including, for example, MOSgated devices, such as MOSFETs and IGBTs.
An active switch bridge, for example, a switch bridge employing MOSFETs and/or IGBTs, may be advantageous with respect to diode bridges, since the channel of a MOSFET and/or IGBT carries the electrical current, as opposed to the diode of the diode bridge. In this advantageous manner, active switch bridges employing MOSFETs and/or IGBTs may better reduce conduction losses.
However, to properly operate an active switch bridge employing MOSFETs and/or IGBTs, signals for the gate nodes of the MOSFETs and/or IGBTs should be generated at appropriate times relative to the sinusoidal voltage source.
Furthermore, if the sinusoidal source produces phase voltages with significant inductances, switching losses may result in operation of a bridge circuit, in which proper control signal timing is not provided. Therefore, it may be advantageous to detect more optimum time instants for the turn-on and turn-off of the gate nodes of the MOSFETs and/or IGBTs.
To overcome these and other disadvantages of prior art rectification circuits, an exemplary embodiment of the present invention provides a rectifying circuit and method to produce a DC output by rectifying a sinusoidal source having a plurality of output phase voltages and a plurality of phase-to-phase voltages, the rectifying circuit including a bridge circuit coupled to the output phase voltages, the bridge circuit having a plurality of switches; and a control circuit coupled to the output phase voltages and to the bridge circuit, the control circuit being configured to control the switches in accordance with respective absolute values of the phase-to-phase voltages; in which the output phase voltages are rectified to produce the DC output.
The absolute values of phase-to-phase voltages may be determined in accordance with the output phase voltages each phase-to-phase voltage representing the voltage across two of the output phase voltages.
By comparing the absolute values of the phase-to-phase voltages, an exemplary rectifying circuit according to the present invention may turn on and/or turn off the switches of the bridge circuit at appropriate times to properly rectify the sinusoidal source and produce the DC output. For example, the exemplary rectifying circuit according to the present invention may operate respective pairs of switches at appropriate times in accordance with the magnitudes of the output phase voltages and the relative magnitudes of the absolute values of the phase-to-phase voltages.
If the sinusoidal source includes significant inductance, rectification of the 3-phase sinusoidal AC source 125 may be improved by providing additional exemplary timing circuitry according to the present invention to better control the switches. In this manner, the control circuit may perform switch turn-off in diode mode (e.g., MOSFET switches) by keeping the switches turned off, and by estimating the period of the sinusoidal source. With the period information, the turn-off commutation times may be estimated, and a delay may be provided, so that turn-off of the switches occurs before the end of the sinusoidal period.